Mobile/portable devices in particular, but also other electronic communication devices are widely used. For proper communication, features such as high linearity and low noise are desired, and features like low power consumption and versatility are also desired, but these groups of features may often contradict each other. For instance, to reach high linearity and low noise figure often leads to large consumption of power, but in the mobile and portable devices, battery capacity in the devices is normally limited for portability reasons, which puts demands on low power design.
Supply voltage downscaling is a trend in modern mobile/portable device design for reducing the power consumed by logic circuits, which is advantageous as more extended features and functionalities are provided, but it creates also a serious challenge for meeting the linearity requirement because of reduced voltage headroom for handling large interference signals. In the presence of interference, a receiver can be desensitized or even blocked if the linearity is poor and the interference is strong.
Radio receiver circuits normally comprise a low noise amplifier connected to an antenna and outputting an amplified signal with enough gain to a mixer circuit for providing a baseband signal. It is desirable for the radio receiver to have good linearity and low noise figure, and to achieve this, a sharp and narrow band pass filter is helpful in radio frequency as it attenuates unwanted interferences. When the number of defined radio bands in wireless radio systems increases, such as for the LTE, each radio band needs to be taken care of. One radio frequency narrow band pass filter implemented by acoustic devices, such as a SAW filter, cannot cover many bands because its inherent resonate frequency. Thus, the radio receiver circuit requires a plurality of filters in the front of low noise amplifier, preferably connected through switches. The insertion loss in the switches degrades the sensitivity of the receiver, and also the cost and area increase are issues. If the radio band pass filter can be made tunable, fewer filters are required. Unfortunately, tunable filters often have poor attenuation in stop bands, and this calls for better linearity in radio receiver front-end, and the unwanted interference signals can be suppressed by low pass filters after down-conversion in mixer. The radio receiver circuit should also be suitable for different conditions, e.g. different use or different signal conditions.
Biasing and filtering can be used for adapting to different signal conditions or uses. However, heavy biasing can be power consuming, and filters can be both expensive and space consuming. Where economic constraints in sense of energy, space and costs, the radio receiver circuit normally needs to be a compromise between the demands and the economic constraints. The designer of the radio receiver circuit then normally designs the circuitry for a worst signal case, which sets the energy consumption for any signal case. Similar applies for filters, mixers, analog-to-digital converters, etc. which may be a part of the radio receiver circuit.
It is therefore a desire to provide a radio receiver circuit capable of adaption.